The present invention relates generally to cooling holes in gas turbine engine components, and more particularly to a method of forming such holes.
Cooling holes are formed in gas turbine components such as vanes, blades and shrouds for transporting film cooling air through the component to cool the component and to form a fluid barrier between the component and hot gases traveling through a main flowpath of the engine. Frequently, these cooling holes are formed by aiming a laser at a selected point on the component for a predetermined period of time to burn a hole through the component. The laser is then aimed at another selected point on the component for a predetermined period of time to burn another hole in the component. This process is repeated to form all the cooling holes in the component. The period of time during which the laser is aimed at particular points is determined by evaluating holes made previously in other components.
Conventional lasers produce holes having large variations in flow rate. Thus, relying on historical data to determine the period of time to burn each hole results in large variations in cooling flow rates which ultimately reduce the effectiveness of the cooling. To compensate for worst case cooling flows, more air must be directed through the cooling holes. Directing more cooling air through the holes reduces the overall engine efficiency. Thus, the variability in cooling hole flow rates adversely affects overall engine performance.
Further, when conventional lasers are used to form holes in some components having internal cavities (e.g., turbine vanes and blades), fillers such as wax, plastics or ceramics must be injected in the cavities to prevent the laser from burning a hole through the wall at the opposite side of the cavity. These fillers must be removed from the cavities after the holes are formed. As a result, using fillers increases the time and expense required to form the holes.
Among the several features of the present invention may be noted the provision of a method of forming cooling holes in a gas turbine engine component. The method includes the steps of forming a hole in the component extending between a first surface of the component and a second surface of the component opposite the first surface and supplying pressurized air to the hole from the second surface of the component. The method also includes the step of sensing a parameter representative of air flow through the hole. Further, the method includes enlarging the hole until the sensed parameter represents a preselected air flow rate through the hole.
In another aspect, a method of the present invention includes the step of aiming a laser beam at a first surface of the component to form a hole in the component extending between the first surface of the component and a second surface opposite the first surface. In addition, the method includes the steps of supplying pressurized air to the hole from the second surface of the component and sensing a pressure of the air entering the hole. The method also includes the step of stopping the laser beam after the sensed pressure meets a predetermined value representing a preselected air flow rate through the hole.
In yet another aspect of the present invention, the method includes the step of directing a pulsing laser at the component. The method also includes the steps of adjusting the laser to have a pulse frequency of between about 100 hertz and about 100 megahertz, adjusting the laser to have a pulse energy of between about 0.001 joules and about 5 joules, and adjusting the laser to have a pulse duration of between about 10 picoseconds and about 100 microseconds.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.